Quantitation of trace betamethasone or dexamethasone in dexamethasone or betamethasone active pharmaceutical ingredients by reversed-phase high-performance liquid chromatography.

Adequate separation is essential for the quantitation of trace amounts of dexamethasone that are typically found in betamethasone active pharmaceutical ingredients and vice versa. In this paper, we describe three simple and efficient high-performance liquid chromatography methods from which true baseline separations between betamethasone and dexamethasone are achieved even when the concentration ratios between these two epimers are larger than 2000:1. One method is developed on a 5 cm ACE C8 column that uses water and acetonitrile as the mobile phase and 20 mM beta-cyclodextrin as the mobile phase additive. The resolution factor between betamethasone and dexamethasone is 3.3. The second method is developed on a 10 cm ACE C8 column that uses water and acetonitrile as the mobile phase, in which the resolution factor between the epimers is 2.7. The third method is developed on a 10 cm ACE C8 column using water and tetrahydrofuran as the mobile phase, in which the resolution factor between the epimers is 3.1. Preliminary validation studies are carried out for the second and third methods.